Atomic Layer Deposition (ALD), originally known as Atomic Layer Epitaxy (ALE), is an advanced variation of CVD. ALD processes are based on sequential self-saturated surface reactions. Examples of these processes are described in detail in U.S. Pat. Nos. 4,058,430 and 5,711,811. The described deposition processes benefit from the usage of inert carrier and purging gases, which make the system fast. Due to the self-saturating nature of the process, ALD enables almost perfectly conformal deposition of films on an atomically thin level.
The technology was initially developed for conformal coating of substrates for flat panel electroluminescent displays that desirably exhibited high surface area. More recently, ALD has found application in the fabrication of integrated circuits. The extraordinary conformality and control made possible by the technology lends itself well to the increasingly scaled-down dimensions demanded of state-of-the-art semiconductor processing.
While ALD has many potential applications to semiconductor fabrication, integrating these new processes into established process flows can introduce many new issues. Accordingly, a need exists for improved ALD processes.